average lead-time is based on incidence rates after 2 screening rounds
(Norway) or 5 screening rounds or more (Sweden). We compare with the
expected incidence rates when we calculate the average lead-time, and have
adjusted for an underlying incidence increase by using regression analysis
modelling the underlying incidence increase.
Because the observed average lead-time in the screening
programme is smaller than in the randomized screening trials and that the
rate of interval cancers is higher, it is likely that reduction in breast
cancer mortality rates will be small than in the randomized screening trials
(mortality reduction in the screening trials varies between 0 and 30%).